From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id E982EC54E58 for ; Tue, 12 Mar 2024 08:50:00 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6ABC28D0020; Tue, 12 Mar 2024 04:50:00 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 633488D0017; Tue, 12 Mar 2024 04:50:00 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4D3FE8D0020; Tue, 12 Mar 2024 04:50:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 369258D0017 for ; Tue, 12 Mar 2024 04:50:00 -0400 (EDT) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 10F5A1A04D9 for ; 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imf04.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf04.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1710233398; a=rsa-sha256; cv=none; b=V0QAIDXWDmdhE9OX664271/txkmMEv1UZghlQ4wB4jvyok7aviW/9fAE1Qlsp1ISlK/BXc Lt94J9rkFVmXHdgKf6i8yo5yCGXdDiTnjrV660TuYJ3WhAyWHoRbQpd7kvgwMpncMkPCoA GZuIaq9eZnRiutVouz2pAA/QprsTIzM= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B67871007; Tue, 12 Mar 2024 01:50:34 -0700 (PDT) Received: from [10.57.68.246] (unknown [10.57.68.246]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 560473F762; Tue, 12 Mar 2024 01:49:55 -0700 (PDT) Message-ID: <28914585-80bd-4308-b3aa-dd0dbb2cb201@arm.com> Date: Tue, 12 Mar 2024 08:49:53 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 0/6] Swap-out mTHP without splitting Content-Language: en-GB To: "Huang, Ying" Cc: Andrew Morton , David Hildenbrand , Matthew Wilcox , Gao Xiang , Yu Zhao , Yang Shi , Michal Hocko , Kefeng Wang , Barry Song <21cnbao@gmail.com>, Chris Li , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240311150058.1122862-1-ryan.roberts@arm.com> <878r2n516c.fsf@yhuang6-desk2.ccr.corp.intel.com> From: Ryan Roberts In-Reply-To: <878r2n516c.fsf@yhuang6-desk2.ccr.corp.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 703C340009 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: zobpoyq7mhmoe3irae1snaub5itxgnea X-HE-Tag: 1710233398-109021 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 12/03/2024 08:01, Huang, Ying wrote: > Ryan Roberts writes: > >> Hi All, >> >> This series adds support for swapping out multi-size THP (mTHP) without needing >> to first split the large folio via split_huge_page_to_list_to_order(). It >> closely follows the approach already used to swap-out PMD-sized THP. >> >> There are a couple of reasons for swapping out mTHP without splitting: >> >> - Performance: It is expensive to split a large folio and under extreme memory >> pressure some workloads regressed performance when using 64K mTHP vs 4K >> small folios because of this extra cost in the swap-out path. This series >> not only eliminates the regression but makes it faster to swap out 64K mTHP >> vs 4K small folios. >> >> - Memory fragmentation avoidance: If we can avoid splitting a large folio >> memory is less likely to become fragmented, making it easier to re-allocate >> a large folio in future. >> >> - Performance: Enables a separate series [4] to swap-in whole mTHPs, which >> means we won't lose the TLB-efficiency benefits of mTHP once the memory has >> been through a swap cycle. >> >> I've done what I thought was the smallest change possible, and as a result, this >> approach is only employed when the swap is backed by a non-rotating block device >> (just as PMD-sized THP is supported today). Discussion against the RFC concluded >> that this is sufficient. >> >> >> Performance Testing >> =================== >> >> I've run some swap performance tests on Ampere Altra VM (arm64) with 8 CPUs. The >> VM is set up with a 35G block ram device as the swap device and the test is run >> from inside a memcg limited to 40G memory. I've then run `usemem` from >> vm-scalability with 70 processes, each allocating and writing 1G of memory. I've >> repeated everything 6 times and taken the mean performance improvement relative >> to 4K page baseline: >> >> | alloc size | baseline | + this series | >> | | v6.6-rc4+anonfolio | | >> |:-----------|--------------------:|--------------------:| >> | 4K Page | 0.0% | 1.4% | >> | 64K THP | -14.6% | 44.2% | >> | 2M THP | 87.4% | 97.7% | >> >> So with this change, the 64K swap performance goes from a 15% regression to a >> 44% improvement. 4K and 2M swap improves slightly too. > > I don't understand why the performance of 2M THP improves. The swap > entry allocation becomes a little slower. Can you provide some > perf-profile to root cause it? I didn't post the stdev, which is quite large (~10%), so that may explain some of it: | kernel | mean_rel | std_rel | |:---------|-----------:|----------:| | base-4K | 0.0% | 5.5% | | base-64K | -14.6% | 3.8% | | base-2M | 87.4% | 10.6% | | v4-4K | 1.4% | 3.7% | | v4-64K | 44.2% | 11.8% | | v4-2M | 97.7% | 13.3% | Regardless, I'll do some perf profiling and post results shortly. > > -- > Best Regards, > Huang, Ying > >> This test also acts as a good stress test for swap and, more generally mm. A >> couple of existing bugs were found as a result [5] [6]. >> >> >> --- >> The series applies against mm-unstable (d7182786dd0a). Although I've >> additionally been running with a couple of extra fixes to avoid the issues at >> [6]. >> >> >> Changes since v3 [3] >> ==================== >> >> - Renamed SWAP_NEXT_NULL -> SWAP_NEXT_INVALID (per Huang, Ying) >> - Simplified max offset calculation (per Huang, Ying) >> - Reinstated struct percpu_cluster to contain per-cluster, per-order `next` >> offset (per Huang, Ying) >> - Removed swap_alloc_large() and merged its functionality into >> scan_swap_map_slots() (per Huang, Ying) >> - Avoid extra cost of folio ref and lock due to removal of CLUSTER_FLAG_HUGE >> by freeing swap entries in batches (see patch 2) (per DavidH) >> - vmscan splits folio if its partially mapped (per Barry Song, DavidH) >> - Avoid splitting in MADV_PAGEOUT path (per Barry Song) >> - Dropped "mm: swap: Simplify ssd behavior when scanner steals entry" patch >> since it's not actually a problem for THP as I first thought. >> >> >> Changes since v2 [2] >> ==================== >> >> - Reuse scan_swap_map_try_ssd_cluster() between order-0 and order > 0 >> allocation. This required some refactoring to make everything work nicely >> (new patches 2 and 3). >> - Fix bug where nr_swap_pages would say there are pages available but the >> scanner would not be able to allocate them because they were reserved for the >> per-cpu allocator. We now allow stealing of order-0 entries from the high >> order per-cpu clusters (in addition to exisiting stealing from order-0 >> per-cpu clusters). >> >> >> Changes since v1 [1] >> ==================== >> >> - patch 1: >> - Use cluster_set_count() instead of cluster_set_count_flag() in >> swap_alloc_cluster() since we no longer have any flag to set. I was unable >> to kill cluster_set_count_flag() as proposed against v1 as other call >> sites depend explicitly setting flags to 0. >> - patch 2: >> - Moved large_next[] array into percpu_cluster to make it per-cpu >> (recommended by Huang, Ying). >> - large_next[] array is dynamically allocated because PMD_ORDER is not >> compile-time constant for powerpc (fixes build error). >> >> >> [1] https://lore.kernel.org/linux-mm/20231010142111.3997780-1-ryan.roberts@arm.com/ >> [2] https://lore.kernel.org/linux-mm/20231017161302.2518826-1-ryan.roberts@arm.com/ >> [3] https://lore.kernel.org/linux-mm/20231025144546.577640-1-ryan.roberts@arm.com/ >> [4] https://lore.kernel.org/linux-mm/20240304081348.197341-1-21cnbao@gmail.com/ >> [5] https://lore.kernel.org/linux-mm/20240311084426.447164-1-ying.huang@intel.com/ >> [6] https://lore.kernel.org/linux-mm/79dad067-1d26-4867-8eb1-941277b9a77b@arm.com/ >> >> Thanks, >> Ryan >> >> >> Ryan Roberts (6): >> mm: swap: Remove CLUSTER_FLAG_HUGE from swap_cluster_info:flags >> mm: swap: free_swap_and_cache_nr() as batched free_swap_and_cache() >> mm: swap: Simplify struct percpu_cluster >> mm: swap: Allow storage of all mTHP orders >> mm: vmscan: Avoid split during shrink_folio_list() >> mm: madvise: Avoid split during MADV_PAGEOUT and MADV_COLD >> >> include/linux/pgtable.h | 28 ++++ >> include/linux/swap.h | 33 +++-- >> mm/huge_memory.c | 3 - >> mm/internal.h | 48 +++++++ >> mm/madvise.c | 101 ++++++++------ >> mm/memory.c | 13 +- >> mm/swapfile.c | 298 ++++++++++++++++++++++------------------ >> mm/vmscan.c | 9 +- >> 8 files changed, 332 insertions(+), 201 deletions(-) >> >> -- >> 2.25.1